sion is generally positioned about 1.5 to 2 cm from the midline.

 

For bilateral decompression, the skin incision is generally positioned 3 to 4 cm lateral to the midline to allow angulation of the tubular retractor across the midline to reach the contralateral side of the spinal canal.

 

A small Cobb elevator is used to elevate the periosteum at the site of the operative exposure (TECH FIG 2A). We prefer to use this rather than dilation over a K-wire, which has the risk of penetrating the dura and is less effective in creating the working space adjacent to the lamina.

 

Dilators are placed through the incision to expand the operative portal (TECH FIG 2B).

 

A tubular retractor of appropriate length is selected and placed over the dilators to the level of the spine (TECH FIG 2C).

 

 

 

TECH FIG 1 • Spinal needle is used to demarcate the proposed location for the surgical incision.

 

 

 

TECH FIG 2 • A. Use of a Cobb elevator to perform subperiosteal dissection. B. Serial dilators are placed to allow placement of the tubular retractor. C. Placement of the tubular retractor. D. Lateral fluoroscopic image to confirm appropriate level and position of the tubular retractor.

 

 

The diameter of the tubular retractor used depends on the nature of the planned surgical procedure. As a general rule, a 14- to 18-mm diameter tubular retractor is used for a microdiscectomy procedure, whereas an 18- to 20-mm tubular retractor is used for spinal stenosis cases.

 

The tubular retractor is secured to the table-mounted retractor holder, and the position of the retractor is verified with lateral fluoroscopy (TECH FIG 2D).

 

If necessary, the position of the tubular retractor is adjusted to allow optimal access to the spinal pathology.

 

Use of a sharp K-wire prior to sequential dilation is avoided as an incidental dural puncture can occur.

 

An appropriate length of the tubular retractor should reach from the skin edge to the spine to minimize soft tissue creep at the base of the retractor.

 

05

 

 

 

TECH FIG 3 • A. Positioning of the microscope to visualize the tissue at the base of the tubular retractor. B.

Use of the electrocautery to clear soft tissue and expose the bony anatomy.

 

Visualization through the Tubular Retractor

 

An operative microscope is focused on the tissue at the base of the tubular retractor (TECH FIG 3A).

 

The residual soft tissue at the base of the tubular retractor should be resected with electrocautery to allow good visualization of the bony elements (TECH FIG 3B).

 

Care should be taken to avoid injury to the facet joint capsule during soft tissue clearance.

Ipsilateral Decompression

 

Before the decompression begins, the inferior edge of the lamina, underlying ligamentum flavum, and medial portion of the facet joint should be identified.

 

It is helpful to palpate the lateral edge of the pars intra-articularis to avoid excessive resection of bone, which could result in an iatrogenic pars fracture.

 

 

The ligamentum flavum is released from the undersurface of the lamina using a curved curette. The medial lamina is removed using a Kerrison rongeur.

 

The ligamentum flavum is traversed with a straight curette by dividing the ligamentum in line with its fibers.

 

The ligamentum flavum is resected as necessary to visualize and remove the spinal pathology.

 

The pedicle is identified by palpation within the spinal canal and used as a landmark for identification of the spinal pathology.

 

The ventral surface of the spinal canal and intervertebral discs can be visualized by gentle retraction of the dura.

 

Any sequestered disc material is removed by “sweeping” the free disc fragments into the laminotomy site using a ball-tipped probe.

 

Extruded disc material is generally removed by breaking the thin, inflammatory membrane over the herniation with a Penfield no. 4 instrument and working through the existing annular tear.

 

The use of large annular incisions is discouraged, as they may predispose to recurrent disc herniation.

 

If lateral recess stenosis is present, the medial portion of the superior articular process is trimmed using a curved-tip Kerrison rongeur.

 

Ipsilateral foraminal stenosis can also be addressed by using a curved-tip Kerrison rongeur to trim the superior tip of the superior articular process.

 

After an adequate decompression of the neural elements has been achieved and confirmed with palpation using a ball-tipped probe, hemostasis of the wound should be achieved prior to closure.

 

Avoid overthinning the inferior articular process or pars interarticularis, which may fracture, leading to instability or persistent pain.

 

If the high-speed burr (drill) is to be used to thin the bone prior to resection, leave the ligamentum flavum intact during drilling to protect the dura (TECH FIG 4). We prefer to use a 3-mm round burr rather than a matchstick style of burr, as it is felt to be more controllable, especially when “end cutting.”

 

Palpate between the dura and the overlying bone to ensure that an adequate plane exists prior to resection of the bone, as this will lessen the risk of an iatrogenic dural laceration.

 

Neovascularization around the nerve root can easily be appreciated while working under the microscope and is a good clinical sign of a symptomatic lesion.

 

 

 

TECH FIG 4 • Use of a high-speed burr/drill to thin the lamina.

 

 

 

Bilateral Decompression through a Unilateral Tubular Approach

06

 

When stenotic changes affect both sides of the spinal canal and cause bilateral neurogenic symptoms, a bilateral decompression of the neural elements should be performed (TECH FIG 5A).

 

The side of the incision is generally chosen to allow optimal access to the pathology, remembering that foraminal stenosis is often easiest to decompress on the contralateral side.

 

The incision is localized in a fashion similar to the unilateral decompression but is placed 3 to 4 cm lateral

to the midline to allow the tubular retractor to be angulated to reach the contralateral side of the spinal canal.

 

After docking the tubular retractor on the lamina and confirming the localization of the tubular retractor with fluoroscopy, an ipsilateral bony laminotomy is performed, leaving the ligamentum in place.

 

The tubular retractor is then angled toward the contralateral side of the spinal canal and the operating table is tilted to provide the most direct microscopic visualization of the contralateral side.

 

Drilling is carried out to provide access to the contralateral side of the spinal canal by removal of the base of the spinous process and the undersurface of the contralateral lamina.

 

 

 

TECH FIG 5 • A. Bilateral decompression of the spinal canal is accomplished by drilling away the base of the spinous process and traversing to the contralateral side of the spinal canal. The contralateral facet is trimmed as needed to decompress the spinal canal. The tube is then redirected, and the ipsilateral side of the spinal canal is decompressed until the dura is free of any compression. B. Adequate decompression is achieved when no further compression of the dura is present.

 

 

As the drilling proceeds, the surgeon will notice the cancellous bone of the inferior articular process.

 

The drilling should continue until the facet joint is thin enough that it can be trimmed (medial facetectomy) with a Kerrison rongeur.

 

Throughout drilling, the ligamentum flavum should be preserved to protect the underlying dura.

 

On the contralateral side, the ligamentum flavum is released ventral to the facet joint, and the thickness of the residual facet joint can be palpated and assessed.

 

After the facet joint is sufficiently thinned and drilling is completed, a curette is used to release the bony attachments of the ligamentum flavum, which is then removed.

 

 

The contralateral pedicle is identified by palpation. The exiting and traversing nerve roots are identified.

 

Bone and ligament decompression is achieved as needed to decompress the neural structures (TECH FIG 5B).

 

After completion of the contralateral decompression, the tubular retractor is wanded back to the ipsilateral side. Decompression of the ipsilateral side is achieved in a similar manner as described.

 

Meticulous hemostasis is performed, followed by tube withdrawal and wound closure.

Wound Closure

Deep tissue (thoracolumbar fascia, if possible) is closed with interrupted suture followed by closure of the subcutaneous tissue and skin.

The subcutaneous incision is infiltrated with a long-acting local anesthetic agent, and a surgical dressing is placed.

 

 

07

PEARLS AND PITFALLS

 

• Localize the incision fluoroscopically.

   

• Use a small Cobb elevator to separate the soft tissues from the lamina prior to inserting the tubular retractor.

   

• Use a surgical microscope for optimal visualization of the surgical field.

   

• Palpate the plane of the nerve root prior to bone removal to reduce the odds of a dural tear.

   

• Keep the ligamentum flavum intact during use of the surgical drill to reduce the risk of dural injury.

   

• Ensure adequate decompression of the neural elements of direct palpation and visualization.

   

• Ensure meticulous hemostasis at the conclusion of the procedure.

 

 

POSTOPERATIVE CARE

Routine postanesthesia recovery is performed.

The patient is then mobilized for ambulation and activities of daily living.

Discharge is generally performed on the day of surgery. A 30-minute per day walking program is recommended.

Pain management is achieved with either a mild oral narcotic or an over-the-counter medication, such as ibuprofen or acetaminophen, depending on the patient's individual pain control requirements.

An office visit and wound check is performed 10 to 14 days after surgery.

Early outpatient physical therapy to assist in rehabilitation is often recommended.

 

 

OUTCOMES

Studies have reported improved outcomes with surgery when compared to nonoperative modalities with respect to walking, endurance, and pain control.1,2,12

Minimally invasive procedures have been shown to provide symptomatic relief at least equivalent to open procedures and are associated with reduced blood loss and shorter hospital stays.4,5,8,9,10,11

 

 

With a minimally invasive approach, less blood loss, less postoperative pain, and a shorter hospitalization are anticipated.3,6,9

 

 

 

COMPLICATIONS

As with all surgical procedures, complications occur with minimally invasive decompression procedures.

The incidence of problems can be minimized, with careful technique and experience with these procedures.

The incidence of dural tear varies but has been reported to be as high as 16% in one study. No long-term

sequelae were noted in these patients.6 When using a tubular retractor, very little soft tissue dead space is created, and thus the incidence of pseudomeningocele or dural cutaneous fistula is very low even if formal dural suture repair is not used.

Small dural tears with no nerve rootlet extrusion may be successfully treated with a small pledget of Gelfoam followed by dural sealant.12

Larger tears or those with exposed nerve roots should undergo a formal dural repair with suture in a watertight fashion.

Suture repair should be accomplished working through the tubular retractor using a micropituitary instrument as a needle holder and using double-armed 6-0 Gore-Tex suture. An arthroscopic knot pusher is used to tie knots during the repair.

Infection rates from tubular decompression surgery are very low. In the rare event of a wound infection, treatment with débridement and appropriate antibiotic therapy should be employed.

 

CONCLUSION

Minimally invasive surgery for lumbar spinal stenosis is an effective procedure with many advantages compared with traditional open lumbar decompression.

 

 

REFERENCES

1. Atlas SJ, Keller RB, Robson D, et al. Surgical and nonsurgical management of lumbar spinal stenosis: four-year outcomes from the Maine Lumbar Spine Study. Spine 2000;25(5):556-562.

    

    

2. Atlas SJ, Keller RB, Wu Y, et al. Long-term outcomes of surgical and nonsurgical management of lumbar spinal stenosis: 8-10 year results from the Maine Lumbar Spine Study. Spine 2005;30(8):936-943.

    

    

3. Asgarzadie F, Khoo LT. Minimally invasive operative management for lumbar spinal stenosis: overview of early and long-term outcomes. Orthop Clin North Am 2007;38(3):387-399.

    

    

4. Benz RJ, Garfin SR. Current techniques of decompression of the lumbar spine. Clin Orthop Relat Res 2001;(384):75-81.

    

    

5. Guiot BH, Khoo LT, Fessler RG. A minimally invasive technique for decompression of the lumbar spine. Spine 2002;27(4):432-438.

    

    

6. Khoo LT, Fessler RG. Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis. Neurosurgery 2002;51(suppl 5): S146-S154.

    

    

7. Palmer S, Turner R, Palmer R. Bilateral decompression of lumbar spinal stenosis involving a unilateral approach with microscope and tubular retractor system. J Neurosurg 2002;97(2 suppl):213-217.

    

    

8. Park P, Foley KT. Minimally invasive transforaminal lumbar interbody fusion with reduction of spondylolisthesis: technique and outcomes after a minimum of 2 years' follow-up. Neurosurg Focus 2008; 25(2):E16.

    

    

9. Podichetty VK, Spear J, Isaacs RE, et al. Complications associated with minimally invasive decompression for lumbar spinal stenosis. J Spinal Disord Tech 2006;19(3):161-166.

    

    

10. Riew KD, Rhee JM. Microsurgical techniques in lumbar spinal stenosis. Instr Course Lect 2002;51:247-253.

     

     

11. Rosen DS, O'Toole JE, Eichholz KM, et al. Minimally invasive lumbar spinal decompression in the elderly: outcomes of 50 patients aged 75 years and older. Neurosurgery 2007;60(3):503-509.

     

     

12. Turner JA, Ersek M, Herron L, et al. Surgery for lumbar spinal stenosis. Attempted meta-analysis of the literature. Spine 1992;17(1):1-8.